Drilling tests under Perth indicate favourable conditions for new railway

20/3/03
Extensive testing under inner city Perth has indicated that the construction of tunnels for the Perth to Mandurah railway line should not present any major problems.
Planning and Infrastructure Minister Alannah MacTiernan today said the investigations had not revealed anything that was unexpected.
"If anything, the updated information provides a more favourable geological model than the earlier one," the Minister said.
"As was expected, the testing confirmed that the majority of the bored tunnelling will be within a sand and clay layer.
"We are confident that the tunnelling should be relatively straightforward and without any nasty surprises."
Ms MacTiernan said risk evaluation was of major importance.
"Given the nature and extent of underground works associated with the city project, encountering unforeseen ground conditions represents the greatest single risk confronting the project," she said.
"To minimise this risk it is critical that information about underground conditions is of the highest possible quality."
The Minister said late last year, Golder Associates was awarded a contract for geotechnical and hydrogeological investigation.
The company's brief was to provide a detailed description of the geology and groundwater conditions in the project area.
Since then there has been:

• underground testing at 50 locations to probe downwards to identify varying strengths of layers of different ground types; and

• drilling of 15 boreholes for geological sampling and the establishment of nine bores for groundwater monitoring.

There was also pump testing at three borehole locations to determine groundwater behaviour, marking the first detailed study of groundwater behaviour in the central business district.
Ms MacTiernan said additional testing was required to address specific areas of concern including identifying buried objects.
The extra testing was also necessary to test for contamination, assist in tunnel boring machine selection and provide more specific information to even further reduce the risk of unforeseen conditions.
The second phase of testing will start early next month (April) and should be completed by the end of June (2003).
Boring of the underground railway tunnels is scheduled to start late next year (2004).

Minister's office: 9213 6400